?The retention and increase of uremic toxin will lead to a series of uremic symptoms, which will affect many systems of the whole body, and lead to the decline of patients' quality of life and high mortality. In 2003, the European Uremic Working Group classified uremic toxins into three groups according to their physical chemistry properties: water-soluble small molecule compounds, protein-binding compounds, and middle molecule compounds. With the new understanding of uremic solutes, the new data of sources and the development of hemodialysis methods and membrane materials, the previous classification can not fully adapt to the new progress in the field of blood purification. Accordingly, in november-december 2020, Claudio R, as president of the General Assembly, convened an expert meeting and prepared an expert consensus that provided new insights into the definition and classification of uremic toxin  tails the expert group's consensus recommendations for new definitions and more clinically oriented new classifications of uremic toxins.